The present disclosure relates to the manufacturing of semiconductor devices. More specifically, the disclosure relates to etching used in manufacturing semiconductor devices.
During semiconductor wafer processing, silicon containing layers are selectively etched. During the etching of silicon containing layers, it is desirable to measure etch rate, etch CD, etch profile, and etch uniformity from wafer to wafer or chamber to chamber. IR absorption may be used to measure the concentration of a by-product produced by the etch process. Etch by-products, dust, and other contaminants may deposit on optical elements, reducing the accuracy of the measurement of IR absorption, reducing the accuracy of the measurement of by-product concentration. It is desirable to maintain the accuracy of the measurement of by-product concentration.